I have once replaced the caps to the 1900-2 (very much the same as the 1900). There is a huge load of caps (around 60) to be replaced and the 1900 is not the easiest one as it's complicated structure and already hard to open if you don't have instructions.
One interesting point with the 1900 is a tip I heard from Martin (Dillen on this forum). This is how he explained it:
The remaining hum could be due to a too low mains voltage. If your actual mains voltage is just below the switch setting, the Beomaster will often hum a bit. F.e. if set to 240V and mains is only 230V, it will be better to run it at the 220V setting. I know it sounds a bit out of normal practice but the Beomaster will not suffer.
I don't know if this has any help in your case as I would believe the hum to apply to both channels but never knows. If not, I would say it's a fuse relared thing indeed.
But be carefull if you touch the selector. A relative of mine who owns the 1900 was told to switch it back to 220v. (As it hummed in 240v setting). He accidently switched it to 130v setting and plugged it in and switched on even the mains voltage here in Finland is 220v! In this case only the fuse(s) needed to be replaced and the BM works but it might not end as happily every time!
Bang & Olufsen - The art of controlling sound, picture and light